Crispy Vegetable Spring Rolls

Heat 2 tablespoons vegetable oil in a large skillet or wok over high heat until shimmering.
Add the garlic and ginger and stir-fry for 15 seconds until fragrant, being careful not to let them burn.
Add the cabbage, carrots, mushrooms, and bean sprouts and stir-fry for 3 to 4 minutes, until the vegetables soften slightly but still have some crunch.
Stir in the green onions, soy sauce, and sesame oil, then remove the skillet from the heat and let the filling cool completely, about 15 minutes; hot filling will tear the wrappers.
Once cooled, drain any excess liquid from the filling by pressing it gently in a colander or fine mesh strainer.
In a small bowl, mix the cornstarch with 2 tablespoons water to make a sealing paste.
Lay one spring roll wrapper on a clean, dry surface in a diamond orientation with one corner pointing toward you.
Place 2 tablespoons of filling in a horizontal line just below the center of the wrapper.
Fold the bottom corner up and over the filling, then fold in the left and right corners tightly like an envelope.
Roll the wrapper away from you into a tight cylinder, brushing the top corner with the cornstarch paste to seal it closed; repeat with the remaining wrappers and filling.
Pour 4 cups of vegetable oil into a heavy pot and heat over medium heat until a deep-fry thermometer reads 350F.
Carefully lower 3 to 4 spring rolls into the hot oil at a time, without crowding the pot, and fry for 4 to 5 minutes, turning occasionally, until deep golden brown and crisp on all sides.
Remove with a slotted spoon or spider strainer to a plate lined with paper towels to drain; let the oil return to 350F between batches so later rolls do not turn greasy.
Serve hot and crispy with sweet chili sauce for dipping.

Letting the filling cool completely before rolling is critical; warm filling releases steam that turns the wrapper soggy and makes it tear.

Keep an accurate 350F oil temperature with a thermometer; oil that is too cool makes greasy rolls, and oil that is too hot burns the outside before the filling heats through.